Project Summary: My research career goals are to continue to conduct extramurally-funded lentiviral research that addresses important knowledge gaps in both equine and human medicine. Although I have made progress towards accomplishing my goals, my ability to achieve independence as an investigator would be significantly enhanced by this award. The majority of my time will be spent conducting research that dissects the mechanisms of adaptive immune control of EIAV, and I plan to spend a significant amount of time acquiring new research skills and knowledge through collaborations with senior investigators in the Department of Veterinary Microbiology and Pathology. The department has an exceptionally talented group of research faculty, with a long history of acquiring extramural support. The major research focus is infectious diseases (host-parasite interactions) including virology, parasitology, bacteriology, vaccine production, and immunology. The overall goals of the proposed research are to develop immunization methods that induce protective antilentiviral CTL responses in individuals with diverse MHC class I backgrounds, and to define the correlates for neutralizing antibody-mediated protection against continued lentivirus replication. The lentiviral system under study is EIAV in horses. The experiments outlined in this application will first determine if a DNA vaccine encoding conserved Gag-specific epitope clusters, augmented with a plasmid expressing an equine IL-2/lgG fusion protein and followed by a vaccinia vector boost, will induce protective high avidity Gag-specific CTL in horses with diverse MHC class I alleles. Because our vaccine constructs will not encode envelope proteins, protective effects will occur in the absence of neutralizing antibody. Separately, we will identify viral envelope variants that arise during progressive EIAV infection, and we will produce equine monoclonal antibodies (EmAb) that neutralize these variants. We will then determine the requirements for neutralizing antibody-mediated protection by infusing combinations of neutralizing EmAbs to SCID foals, 10 and 14 days post-ElAV challenge. This time frame is relevant to post-HIV-1 exposure prophylaxis, and has been shown in B cell depletion studies to be the time when neutralizing antibodies are involved in SIV control. The equine SCID defect allows the protective effects of neutralizing antibodies directed against multiple naturally-occurring lentivirus escape variants to be tested without the influence of endogenous B and T cell responses. These are experiments that cannot be done in any other lentivirus model system. Relevance: Accomplishing these aims should help define the correlates for CTL- and neutralizing antibody-mediated protection against a naturally-occurring lentivirus infection in a diverse population. The information obtained from the proposed studies should have implications for HIV-1 vaccine design, where experiments of this type are not possible.